Activation of hydrogen by rhodium complexes containing sulphide ligands. Part III. Studies involving substrate effects and ligand effects

Abstract

The kinetics are reported for the hydrogenation of trans-cinnamic acid and maleic acid using RhCl₃(Et₂S)₃ and RhCl₃[(PhCH₂)₂S]₃, respectively, as catalysts in NN′-dimethylacetamide solution under mild conditions. Ligand-dissociation reactions of rhodium(I)–olefin intermediates appear important and are thought to relieve steric crowding to assist the oxidative addition of cis-hydrides. An unusual limiting hydrogenation rate, independent of the totarhodium concentration, is explained by inhibition of the dissociation reaction by sulphide ligands, liberated during formation of the rhodium(I) catalyst.